Mobility devices, which include but are not limited to powered wheelchairs and mobility scooters, are an important tool for those with impaired mobility. It is common to provide mobility devices with powered operations to minimise the manual input required from a user. This is especially important in the case of users whose impairment may prevent them from manually operating the mobility device.
Such powered operations may include a traction motor (or similar) to move the mobility device. Another powered operation may be manipulating the position of parts of the seats, for example, adjusting the inclination of the back of the seat of the mobility device.
Mobility devices may incorporate electronic controllers to convert speed and direction commands into voltage to power the electric motors. Such controllers are controlled by users via a user input devices (such as a joystick). Precise control of the motors is required to ensure accurate velocity and steering of the mobility device.
One problem associated with such control is that there needs to be regulation of the achievable rate of acceleration and the achievable rate of turning at various velocities. If the rate of acceleration exceeds a certain threshold (for example, when accelerating the mobility device in a forward direction or accelerating a seat back to a more vertical inclination) this can result in a ‘jerk’. Not only does this affect a user's comfort, but it also could result in mobility device instability. If the rate of turning at a particular velocity exceeds a certain threshold (for example, when turning the mobility device whilst moving forward at high speeds), this may result in excessive yawing and instability. That is to say, if the mobility device is allowed to turn too suddenly there can be a resultant and undesirable instability.
A particular challenge arises for in front wheel drive mobility devices which are dynamically unstable at speed. Once the mobility device starts to yaw, inertial forces tend to increase the yawing effort in proportion to the square of the forward speed. As above, to ensure rotational stability, regulation of the controller and achievable rate of turning at various velocities is important.
It is preferable that these achievable rates are set in accordance to, and do not exceed, the particular user's driving ability. These achievable rates also need to be set in accordance with a particular user's weight and body distribution on their particular mobility device (i.e. their seating position with respect to the wheels). This calibration function is frequently performed by a therapist who may not be technically experienced.
Traditionally to calibrate the mobility device, these achievable rates are programmed into the mobility device controller by manually entering rates of turning for various velocities or joystick deflections or by manually entering rates of acceleration. This can be a tedious process and not particularly intuitive. This is exacerbated by the fact that a number of trials are required to optimise performance of the mobility device. It may not be readily apparent to the programmer (particularly where the programmer has limited previous experience) what parameters should be entered even as a starting. Further, there can be a large number of parameters that need to be programmed, and it may not be immediately apparent to the programmer that there is a mistake or flaw in the parameters as entered.
Another known option to ensure mobility device stability is to use sensors to detect instability and to use this information to limit the operation of the mobility device in some way (for example, by throttling the velocity). A problem associated with this approach is that the sensors may not detect instability before it is too late. Also, such sensors are expensive and add complexity to the mobility device and its wiring.
It is an object of the invention to provide a method for calibrating mobility devices that alleviates at least some of the problems identified above.
It is also an object of the invention to provide a method for calibrating a mobility device that does not rely on a programmer having particular expertise or previous experience, and a method that is intuitive and requiring minimal programmer input, time and cost.
Each object is to be read disjunctively with the object of at least providing the public with a useful choice.
Reference to any prior art in this specification does not constitute an admission that such prior art forms part of the common general knowledge.